Clamping mechanism for draw presses



Dec. 5, 1950 c. G. ELLIS 4 2,532,663

I CLAMPING MECHANISM FOR DRAW PRESSES Filed July s, 1946 To oiher' units INVENTOR CHARLES G. ELLIS BY 7 I v ATTORNEY Patented Dec. 5, 1950 'CLAMPING MECHANISM FOR DRAW PRESSES Charles G. Ellis,'Union, N. J., assignor to The Oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application July 3, 1946, Serial No. 681,371

11 Claims.

This invention relates to mechanisms for clamping work while being operated upon and it is particularly adapted for clampin blanks while being drawn or formed into desired shapes.

During a drawing or forming operation, the marginal portion of a blank is engaged by a draw ring or clamping member which exerts upon the blank a clamping force which is sufficient to hold it firmly but not great enough to prevent it from being drawn into the die or mold. The clamping force must be accurately regulated and some types of work require that the clamping force be less than the force resulting from the weight of the clamping member and associated parts which are often very heavy.

In a hydraulic press, the work is ordinarily clamped by hydraulic clamping motors and, when it is desired that the clamping member exert a clamping force less than that resulting from the weight of the clamping member and associated parts, resistance valves connected to the lower ends of the clamping motors are adjusted to maintain in the lower ends of the clamping motors sufficient pressure to support a part of the weight of the clamping member and associated parts. This method wastes power and causes heating of the motive liquid.

Th primary object of the present invention is to provide a clamping mechanism which may readily be adjusted to vary the clampin force from zero to maximum and which will maintain the clamping force at or near zero without undue waste of power or heating of the motive liquid.

The invention is exemplified by the clamping mechanism shown schematically in the accompanying drawing.

For the purpose of illustration the invention has been shown applied to a hydraulic draw press having a draw ring I extending around a platen 2 which is attached to the rod 3 of the main hydraulic motor 4. Draw ring I is adapted to be urged downward against the work -by a plurality of hydraulic clamping motors 5 of which only two have been shown. Each motor 5 includes a stationary cylinder 6, a difierential piston l fitted in cylinder 8, a piston rod 8 which is fixed to piston and engages or is fixed to draw ring I, and a tail rod 9 which is larger than piston rod 8 and extends through the upper end of cylinder 6. Due to tail rod 9 having a greater cross sectional area than piston rod 8, the lower face or pressure area of piston l is larger than the upper face or pressure area of piston l.

Liquid for causing motors 5 to urge draw ring I against the work is supplied by a pump In of the so called constant pressure type. That is, pump i0 delivers liquid at a predetermined maximum rate until it creates a predetermined maximum pressure and then it automatically reduces its displacement until it is delivering just enough liquid to maintain that maximum pressure constant. Since such pumps are well known, pump H) has not been illustrated in detail and further description thereof is deemed unnecessary.

Pump It: draws liquid through a channel II from a tank l2 and discharges it into a branched supply channel l3 which is connected to the upper ends of all of the clamping motors 5. Channel l3 is also connected by a channel It to the inlet of a bypass valve l5, the outlet of which is connected by a channel IE to tank l2.

Valve l5 has been shown as being spring biased to open position and as being adapted to be closed by a solenoid I1 but it may be operated in any other suitable manner. Pump It will be short circuited when valve I5 is open, as shown, and it will deliver its entire output to the several clamping motors 5 when valve I5 is closed. Valve|5 also permits liquid to escape from the upper ends of motors 5 durin upward movement of draw ring l. I

During operation of the clamping mechanism, pressure is maintained in the lower end of each clamping motor 5 by a pressure control valve 20 which has been shown as being of the type described and claimed in Patent No. 2,267,380.

As shown schematically in the right hand part of the drawing, each valve 20 includes a resist ance valve 2|, which has its inlet connected to the lower end of cylinder 8 as by means of a channel 22 and its outlet connected to tank |2 as by means of a channel 23, and a resistance valve 24 which has its inlet connected to a branch of channel l3 as by means of a channel 25 and its outlet connected to the inlet of resistance valve 2| as by means of a channel 26 and channel 22.

, Resistance valves 2| and 2 4 are simultaneously adjustable inversely to each other. As shown schematically, the threaded stems of valves 2| and 24 are provided, respectively, with nuts 21 and 28 and. an unthreaded part of the stem of valve 2| extends into nut 28 and is fixed for rotation therewith by a set screw 29 so that turning nuts 21 and 28 in one direction or the other will simultaneously increase the resistance of one and decrease the resistance of the other of valves 2| and 24. The resistances of 2| and 24 may be varied relatively to each other by loosening set screw 29 and turning one or the other of nuts Z1. and 28.

In practice however, resistance valves 2| and 24 are arranged within a suitable casing as indicated in the left hand portion of the drawing, the resistances of the two valves are simultaneously varied inversely to each other by turning a knob 28 which corresponds to nut 28, and the resistances of the two valves are varied relatively to each otherby turnin a screw 27 For reasons that will presently appear, channels 22 are connected by a channel 30 and a check valve 3| to tank I2 and a check valve 32 is connected between each channel 22 and the adjacent channel 25.

Operation Draw ring I may be operated hydraulically in both directions by connecting pump I'll to channels I3 and 30 through a reversing valve but for the purpose of illustration it has been shown as being adapted to descend by gravity and to be raised by platen 2. During upward movement of draw ring I, each piston I will draw liquid into the lower end of its cylinder 6 through channels 22 and 30 and check valve 3I- from tank I2 and it will eject liquid from the upper end of cylinder 6 through channels I3 and I4, bypass valve "I5 and channel I6 into tank I2.

When platen 2 reaches its upper position, the press stops with the parts in the positions shown and pump Iii draws liquid through channel I I from tank I2 and discharges it through channels I3 and I4, bypass valve I5 and channel I6 back to tank I2.

When platen 2 moves downward, draw ring will move downward with it and cause each piston 1 to expel liquid from the lower end of its cylin der 6 through channel 22 and check valve 32 into channel 25. A part of this liquid will flow from channel through channel I3 the upper :part of cylinder 6 to keep it flooded and the remainder will flow from channel 25 through channels I3 and I4, bypass valve I5 and channel I6 to tank I2.

Draw ring I continue downward in this manner until it is about to engage the work and then valve I5 is closed by solenoid I'I being energized by means which have not been shown. as such means are well known.

When valve I5 closes, the liquid discharged by pump I0 flows to the upper ends of the several motors 5 and causes the pistons 1 thereof to force draw ring I against the work and to eject liquid from the lower ends of cylinders 6 through channels 22, resistance valves 2| and channels 23 to tank I2. The resistance of each valve 2l' to the flow of liquid therethrough causes the piston 1 associated therewith to create in the lower part of its cylinder 6 a pressure equal tothe resistance of valve 2|. 7

When the work prevents further downward movement of draw ring I, pump pressure willrise to maximum and then pum II) will go to slip stroke; As soon as pump pressure exceeds a predetermined value, valve 24' will open so that, when pump pressure reaches maximum, pump I0 can maintain in the lower part of cylinder 6 a pressure substantially equal to the difference between maximum pressure and the pressure at which valve 24 opens, it being understood that the sum of the resistances of valves 2| and 24 is substantially equal to the maximum pressure created by pump H1.

The upper face of piston is thussubjected to maximum pump pressure and the lower face thereof is subjected to a lower pressureas deter- 4 valve 20. If valve 20 is so adjusted that resistance valve 24 will not open until pump pressure reaches maximum and resistance valve 2| will open at any pressure above zero, there will be substantially no pressure in the lower end of cylinder 6 and piston 1 will exert its maximum clamping force. If valve 20 is so adjusted that resistance valves- 2| and 24' will open at intermediate pressures, valve 2| will maintain in the lower end of cylinder 6 an intermediate pressure which causes the liquid in the lower end of cylinder 8 to exert upon piston i an upward force which opposes the downward force exerted upon piston I by the maximum pressure liquid, thereby reducing the clamping force exerted by piston 1 Since the lower face of piston l is larger than the upper face thereof, valve 2|) may be so adjusted that the liquid in the lower end of cylinder 6 has sufiicient pressure to exert upon piston 1 an upward force which exceeds the downward force and thereby counterbalances a part of the weight of draw ring I'.

The invention herein set forth is susceptible of various modifications and adaptations without departing from the scope of the invention which is hereby claimed as follows:

I claim:

1. In a press having a downward. actingv member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against said work and including a differential piston thelower face of which is larger than the upper face thereof, means for supplying liquid at a substantially constant pressure to the upper end of said motor, and a pressure control valve having two inlets connected to the upper and lower ends of said motor respectively and an outlet connected to exhaust, said valve having means to resist the flow of liquid through said inlets and thereby enable said valve to'maintain inthe lower end of 'said motor apressure lower than said constant pressure in the upper end of said motor.

2. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against said work and including a differential piston the lower face of which is larger than the upper face thereof, means for supplying liquid at a substantially constant pressure to the upper end of saidmotor, and a pressure control valve having two inlets connected to the upper and lower ends of said motor respectively and an outlet connected to exhaust, said valve having means to. resist, the flow of liquid through said inlets and thereby enable said valve to maintain in the lower end of said motor a pressure lower than said constant pressure in the upper end of said motor, said control valve being adjustable to vary the pressure in the lower end of said motor to such an extent that the force exerted by the liquid upon the lower face of said piston is greater than the force exerted upon the upper face of said piston by the liquid in the upper end of said motor.

3. In a press having a downward acting member for clamping work to be operated upon by saidv constant pressure pump connected by a channel;

to the upper end of said motor for supplying motive liquid thereto,-apressure control; valve having two inlets connected to the upper and lower ends of said motor respectively and an outlet connected to exhaust, said valve having means to resist the flow of liquid through said inlets and thereby enable said valve to maintain in the lower end of said motor a pressure lower than said constant pressure in the upperend of said motor, said control valve being adjustable to vary the pressure in the lower end of said motor to such an extent that the force exerted by the liquid upon the lower face ofvsaid piston is greater than the force exerted upon the upper face of said piston by the liquid in the upper-end of said motor, and a bypass valve connected to said channel and adapted whenopen to short circuit said pump and to permit liquid .to escape freely from the upperend of said motor.

4. In a press having a downward acting memher for clamping work to be; operated upon by said press, the combination of a vertical clamping cylinder, a piston arranged within said cylinder, a piston rod extending 'thru the lower end of said cylinder and connecting said piston to said member, a constant pressure pump connected by a channel to the upper end of said cylinder for supplying motive liquid thereto, a pressure control Valve having two inlets connected to the upper and lower ends of said cylinder respectively and an outlet connected to exhaust, saidvalve having means to resist the flow of liquid through said inlets and thereby enable said valve to maintain in the lower end of said cylinder a pressure lower than said constant pressure in the upper end of said cylinder... atail rod larger than said piston rod connected to said piston and extending through the upper end of said cylinder so that said lower pressure in the lower end of said cylinder acts upon an area of said piston greater than the piston area which is subjected to the higher pressure in the upper end of said cylinder, and a bypass valve connected to said channel and adapted when open to short circuit said pump and to permit liquid to escape freely from the upper end of said cylinder.

5. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against said work and including a differential piston the lower face of which is larger than the upper face thereof, means for supplying liquid at a substantially constant pressure to the upper end of said motor, a first resistance valve having its inlet connected to the upper end of said motor and its outlet connected to the lower end of said motor, a second resistance valve having its inlet connected to the lower end of said motor and its outlet connected to exhaust, and means for simultaneously adjusting said resistance valves to vary the resistances thereof inversely to each other.

6. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against said work and including a differential piston the lower face of which is larger than the upper face thereof, a constant pressure pump connected by a channel to the upper end of said motor for supplying motive liquid thereto, a first resistance valve having its inlet connected to the upper end of said motor and its outlet connected to the lower end of said motor, a second resistance valve having its inlet connected to the lower end of said motor and its outlet connected to exhaust,

means for simultaneously adjusting-saidresistance valves to vary the resistances thereof inversely to each other, and a bypass valve connected to said channel and adapted when open to short circuit said pump and to permit liquid to escape freely from the upper end of said motor.

'7. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping cylinder, a piston arranged within said cylinder, a piston rod extending thru the lower end of said cylinder and connecting said piston to said member, a tail rod larger than said, piston rod connected to said piston and extending through the upper end of said cylinder so that the lower face of said piston is larger than the upper face thereof, a constant pressure pump connected by a channel to the upper end of said cylinder for supplying emotive liquid thereto; a first resistance valve having its inlet connected to the upper end of said cylinder and its outlet connected to the lower end of said cylinder, a second resistance valve having its inlet connected to the lower end of said cylinder and its outlet connected to exhaust, means for simultaneously adjustingsaid resistance valves to vary the resistances thereofrinversely to each other, and a bypass valve connected to said channel and adapted when open to short circuit said pump and to permit liquid to escape freely from the upper end of said cylinder.

3. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against saidwork and including a differential piston the lower face of which is larger than the upper face thereof, a constant pressure pump connected by a channel to the upper end of said motor for supplying motive liquid thereto, a pressure control valve having two inlets connected to the upper and lower ends of said motor respectively and an outlet connected to exhaust,'said valve having means to resist the flow of liquid through said inlets and thereby enable said valve to maintain in the lower end of said motor a pressure lower than said constant pressure in the upper end of said motor, and a check valve connected between the two ends of said motor to prevent flow from the upper end to the lower end thereof but permitting flow from the lower end to the upper end thereof during downward movement of said piston.

9. In a press having a downward acting member for clamping work to be operated upon by said press, the combination of a vertical clamping motor for urging said member against said work and including a differential piston the lower face of which is larger than the upper face thereof, a constant pressure pump connected by a channel to the upper end of said motor for supplying motive liquid thereto, a first resistance valve having its inlet connected to the upper end of said motor and its outlet connected to the lower end of said motor, a second resistance valve having its inlet connected to the lower end of said motor and its outlet connected to exhaust, means for simultaneously adjusting said resistance valve to vary the resistances thereof inversely to each other, and a check valve connected between the two ends of said motor to prevent flow from the upper end to the lower end thereof but permitting flow from the lower end to the upper end thereof .during downward movement of said piston.

1'0 In a'downward acting press liaving a platen, means for reciprocating said platen, a member for clamping work to be operated uponby said press and means for causing said member to be moved upward by said platen during the up stroke thereof, the combination of: a vertical clamping motor for urging saidmember against said work and including a differentiarpiston the lower face of which is larger than the upper face thereof, a constantpressure pump-connected by a channel to the upper end of saidmotor for supplying motive liquid thereto, a pressure control valve having two inlets connected to the upper and lower ends of said motor respectively and an outlet connected to exhaust, said control valve having means to resist theflow ofliquid through said inlets and thereby enable said valve to maintain in the lower end of said: motor a pressure lower than said constant pressure in the upper end of said motor, and a bypass valve connected to said channel and "adapted when open to short circuit said pump and to permit liquid to escape freely from the upper end of said 'motor when said clamping member moved upward by said platen.

'11. In a downward acting press having a platen, means for reciprocatingsaid platen, a member for clamping work to be'opera-ted upon by said press and means for causing said member to be moved upward by said platen during the up stroke thereof, the combination or a vertical clamping motor for urging said member againstsaid work and including a differential piston the-lower face of which is larger than the upper face thereof, a constant pressure pump connected 'bya chan- 8 nel to the upper end orsaid motor for supplying motive liquid thereto, a first resistance valve having its inlet connected: to the upper end of said motor and its outlet connected to the lower end: of said motor, a-secondresistance valve-havingits inlet connected to the lower end of said motor-andits outletconnected to exhaust, means for simultaneously adjusting said resistance valves to vary the resistances thereof inversely toeach other, a bypass valve connected to said channel and adapted when open to short circuit said pumprand to permit liquid to escape freely from the upper end of said motor when said clampingmember is moved upward by said platen. and a check valve-connected between the two' ends of said motor to prevent flow from theupper end to the lower end thereof but permitting flowfrom the lower end to the upper end thereof during downward movement of said piston.

CHARLES G. ELLIS.

REFERENCES CITED The "following references are of record in the file of this patent: 

